1. Field of Invention
This invention relates in general to chimney caps, and more particularly to a locking chimney cap for use with clay flue tiles or the like.
2. Discussion of the Prior Art
Chimney caps are commonly used on chimneys to prevent the ingress of rain, snow, birds, rodents and leaves as well as to prevent down-drafts and to reduce the deterioration of mortar in the chimney.
Most clay flue tiles in masonry chimneys are either 200.times.200 mm, 200.times.300 mm, or 300.times.300 mm outside diameter. It is thus readily seen that either the 200 mm or 300 mm dimension exists on most flue tiles. However, each size of flue tile typically also has a different wall thickness dimension. For example, a 200.times.200 mm flue tile is usually 16 mm thick with a tolerance of 3 mm; a 200.times.300 mm flue tile is typically 19 mm thick with a tolerance of 3 mm; while a 300.times.300 mm flue tile is usually 23 mm thick with a tolerance of 3 mm. Furthermore, the outside diameter of the tiles themselves are typically characterized by tolerances of from 0 to 10 mm. These tolerances are normally very difficult to maintain due to different styles and ages of chimneys.
The cumulative effect of the varying wall thicknesses and tolerances is that it is typically very difficult to fit all flue sizes with a chimney cap unless an almost infinitely adjustable mechanical fixing technique is employed.
In most instances, in order to determine the size of chimney cap required for a particular chimney, it is necessary for a person to climb onto the roof and measure the flue size to determine whether or not the chimney conforms to one of the aforementioned standard sizes.
Upon determining the dimensions of the chimney flue tile, the installer then must descend from the roof, purchase an appropriate size of chimney cap, and then climb again onto the roof for installation of the chimney cap.
Some prior art chimney caps require the use of a variety of tools for installation. For example, various prior art arrangements utilize mechanical attachment components such as thumb screws or clamp arrangements.
U.S. Pat. No. 4,697,500 (Hisey) discloses a well known prior art clamp and bracketing chimney cap arrangement utilizing nuts and bolts for fixing the chimney cap to the flue tiles. The Hisey patent suffers from the disadvantage that the various nuts and bolts may become loose resulting in possible dislodgement of the chimney cap.
U.S. Pat. No. 4,482,267 (Widerby) discloses a spring loaded apparatus for mounting a ventilation element in a conduit. No size adjustment is provided in the Widerby patent. Instead, one or several anchor devices are provided on an internal annular ridge, which bear against the inside walls of the conduit.
U.S. Pat. Nos. 2,976,796 (Anthony et al) and 2,805,616 (Roth) disclose additional well known prior art chimney caps for installation into a chimney of standard size. There is no provision in either of the Anthony et al or Roth patents for adapting the chimney cap to flues of different size.
Thus, according to the above-discussed prior art chimney caps, it is typically necessary for the person installing the chimney cap to make at least two or more climbings of the roof with tools in order to install the chimney cap. Multiple climbings of the roof with tools is both tiring and potentially dangerous for the average home owner, particularly in view of the danger of accidentally falling off the roof with each ascent or descent.
Additional prior art chimney caps have been developed for accommodating different sizes of chimney flue tiles, thereby overcoming the prior art disadvantage of requiring two or more climbings onto the roof.
U.S. Pat. No. 841,660 (Barnes) teaches an adjustable locking mechanism consisting of a pair of arms which engage the interior walls of the chimney at the corners thereof, the arms being provided with laterally extending spurs adapted to be driven or otherwise embedded in the mortar. The arms are provided with lateral extensions, the adjacent longitudinal edges of which are provided with teeth or serrations adapted to inter-engage, and thereby lock the arms in an adjusted position. One of the arms is provided with an offset portion to permits sliding movement of the extension of the adjacent arm.
Extending vertically through a lateral ear or lug portion of the supporting bar in Barnes is a pin on which is pivotally mounted a locking member or cam, adapted to engage the smooth edge of the adjacent extension, thereby forcing the teeth into engagement with each other, and thus locking the arms into an adjusted position.
U.S. Pat. No. 4,335,648 (Mitchell) discloses a chimney cap or cowl which is secured by a wing nut. The chimney cowl of Mitchell is self-adjusting to the dimensions of flue tile. However, the installation technique of the wing nut arrangement of Mitchell is fairly complex.
A fundamental disadvantage of such prior art adjustable size chimney caps is that the various locking mechanisms deployed therein are subject to loosening. In particular, since chimney caps are often subjected to strong external forces due to high wind conditions, etc., these prior art chimney caps are prone to accidental dislodgement often resulting in damage to the chimney cap in the event that it falls off the roof.
Moreover, the prior art mechanical screw and nut type of locking mechanisms are subject to corrosion or fouling, making them difficult to remove for chimney cleaning.